1. Field of the Invention
The present invention relates to an electrostatic chuck device for using electrostatic energy to fix semiconductors or conductors like wafers in place by adsorption.
2. Description of the Related Art
Chuck devices are used for fixing a semiconductor wafer in place at a specific site in the processing equipment during the step in which the semiconductor wafer is worked. Devices employing mechanical, vacuum and electrostatic means are available as chuck devices. Of these, an electrostatic chuck device offers the advantages of enabling adsorption even when the wafer is not flat, easy handling, and applicability in a vacuum.
One example of a conventional electrostatic chuck device is disclosed in Japanese Patent Application, Second Publication No. Hei 5-87177. As shown in FIG. 4, in this device, an adhesive layer 2a, insulating film layer 4, adhesive layer 2b, electrode 3b consisting of a thin metallic plate, adhesive layer 2c, and insulating film layer 7 are sequentially laminated onto a metal substrate 1. Wafer 5 is adsorbed to wafer adsorbing surface, which is the upper surface of insulating film layer 7. A temperature adjusting means 6 is formed inside metal substrate 1 for adjusting the temperature by passing through constant temperature water or the like.
FIG. 5 shows the electrostatic chuck device disclosed in Japanese Patent Application, First Publication No. Hei 8-148549. This device is designed so that a relatively thick insulating adhesive layer 2 is formed onto metal substrate 1. An electrode 3a formed of a vapor deposited or plated metal coating is adhered to the bottom surface of an insulating film layer 7, which is adhered on to insulating adhesive layer 2. Semiconductor wafer 5 is then adsorbed to this insulating film layer 7.
It is, by the way, desirable that such devices as these have a high coefficient of thermal conductivity while at the same time maintaining electricity insulating properties. When coefficient of thermal conductivity is low, the efficacy of the temperature adjusting means is insufficient, causing the wafer to experience an abnormal increase in temperature during processing.
In recent years, it has been proposed to improve the ability to transfer heat from the wafer to the metal substrate while at the same time maintaining high electricity insulating properties, by disposing a ceramic plate that has excellent electricity insulating properties and thermal conductivity which is superior to that of resins.
Typically, thermosetting adhesives such as epoxy-type adhesives are used as the adhesive for adhering the ceramic plate. However, epoxy-type adhesives have especially high Young's modulus after hardening and experience volume changes to some extent during hardening.
For this reason, the adhesive is not able to absorb stress which is generated due to different coefficients of thermal expansion between the metal substrate and the ceramic plate, and the adhesive separates from the ceramic plate, particularly at the outer periphery thereof, causing a deterioration in thermal conductivity at these areas of separation. As a result, cooling of the outer periphery of the wafer becomes difficult. In addition, because the ceramic plate employed is typically very thin, when stress is applied on the ceramic plate due to volume changes in the adhesive layers, a variety of problems occur as bowing of the ceramic plate so that there is a deterioration in the flatness of the wafer adsorbing surface, a decrease in the wafer adsorbing force, and significant leaking of the helium gas used for cooling which is supplied in small amounts between the wafer adsorbing surface and the wafer.
As in the conventional examples described above, when made of a resin material, wafer adsorbing surface is gradually worn due to repeated contact with the wafer. In addition, damage or deformation may occur in the wafer adsorbing surface due to foreign objects. Accordingly, the durability of such resin wafer adsorbing surface has not been sufficient.
In addition, there are other problems encountered such as gradual exhaustion and deterioration due to subjection to various reactions and dry etching with plasma during wafer processing, a deterioration in the electricity insulating properties of the electrostatic chuck device over a relatively short period of time due to damage imparted during handling or the like, poor durability, and short life.
Moreover, another problem which occurs is that insulation breaks down when microscopic damage occurs to the adsorbing surface.